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Determining the Rate Law from Experimental Data

Process of using experimental data to determine reaction time

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Winning the Race

Winning the Race

Credit: Wonker
Source: http://www.flickr.com/photos/94056408@N00/2589796154
License: CC BY-NC 3.0

The driver downshifts as he approaches the tight Mulsanne curve leading into the Mulsanne Straight in the Le Mans 24-hour endurance race. He drifts into the turn, then shifts to a higher gear and accelerates leaving the turn. The goal: drive the longest distance in 24 hours and keep the car intact. A combination of speed, careful preparation, and attention to detail are the ingredients to victory.

Why It Matters

  • How fast do you need to drive to win at Le Mans or any other sports car race? The instantaneous speed is not as important as the rate of travel over the entire time of the race. There is no timed segment, just an overall distance within a defined time period. The amount of miles (or kilometers since we’re in France for Le Mans) covered divided by 24 hours gives us the rate. Since the goal is to travel further than anyone else (and the time is fixed), the rate is proportional to the distance traveled.
  • What influences success at Le Mans? The easy answer is to say “The driver makes the difference.” If we look closely at the situation, we will find that there are a number of factors affecting the rate of travel. Since this is a 24-hour race, there needs to be more than one driver. Current rules require three drivers, and the common practice is to rotate them on at two-hour intervals. Then you need one car (that’s obvious). Tires are a big factor, both in terms of quality and quantity. There are several tire changes made due to wear on the tires. In addition, different weather conditions will dictate different types of tires. Finally, a good pit crew is indispensable for success. These team members change tires, refuel the car, make repairs, and manage the strategy for the drivers.
  • Credit: David Merrett
    Source: http://www.flickr.com/photos/davehamster/3956157017/
    License: CC BY-NC 3.0

    The pit crews are constantly working to maintain the car throughout the whole 24 hours [Figure2]


  • The performance on the track is determined by a combination of planning and practice. The materials can be organized, drivers and pit crew trained, fuel obtained – all these things and more can be dealt with ahead of time. But the actual performance is determined by getting out on the track and seeing what works. Do we need to change to softer tires because of the weather (even though that slows the car down)? Adjusting the suspension may give better handling in the turns. Many factors that lead to eventual success must be tested on the track.
  • Watch a video of a sports car race at the link below:


Can You Apply It?

Use the links below to learn more about reaction rates. Then answer the following questions.

  1. How is reaction rate usually measured?
  2. How can you change the rate constant for a reaction?
  3. What are two factors that affect reaction rate in solid and liquid processes?
  4. What is collision theory?
  5. How will increasing the exhaust diameter affect the power of a car?

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Image Attributions

  1. [1]^ Credit: Wonker; Source: http://www.flickr.com/photos/94056408@N00/2589796154; License: CC BY-NC 3.0
  2. [2]^ Credit: David Merrett; Source: http://www.flickr.com/photos/davehamster/3956157017/; License: CC BY-NC 3.0

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